Increasing energy costs from fossil fuels stimulates renewable energy acquisitions. Furthermore, in many countries legal requirements exist to reduce the production of greenhouse emissions, e.g. in the European Union. Since renewable energy is often generated in the form of electric current which could use the existing energy transmission infrastructure, it is necessary for renewable energy converters to match the transmission system parameters. It is, for example, required that electrical energy fed in a power grid matches parameters such as: voltage, frequency and phase angle. Usually, this is achieved by using power inverters that, by means of power electronic commutation circuits, form appropriately shaped one to three-phase currents. The electric current provided by the inverter often contains undesired high frequency components, besides the fundamental 50 Hertz (Hz) or 60 Hz grid frequency. Partial elimination of the high frequency current components is achieved by using filtering circuits, sometimes also referred to as sine-filters. Such filters usually contain inductors in combination with capacitors.
The profitability of renewable energy is determined by the cost of the generation system that includes, among other components, an energy source, e.g. a photovoltaic generator, as well as the inverter, but also by the efficiency of the system. Therefore, any improvements that allow for a reduction of the size and/or the weight of inductive components are within the scope of interest. A reduction in size and/or weight does not only lead to specific material savings, but also to a reduction of power losses.
The document U.S. Pat. No. 7,830,235 describes an integrated inductor arrangement used in a direct-current (DC) input stage for an inverter coupled to a fuel cell. The inductor arrangement contains inductive elements associated with magnetic loops, where adjoining magnetic loops share common core pieces. Thanks to this, the total weight of the integrated inductor arrangement is reduced compared to separated inductors. The solution according to the document U.S. Pat. No. 7,830,235 is intended for a DC/DC-converter. The energy from the DC-source is boosted by transmitting it to the one of the inductive elements and then, after opening the switching elements in the DC-input stage, transferred to a higher voltage. Since the time required for energizing the inductor is longer than the time needed to transfer the energy to the load, the inductor was tripled in order to reduce time without constraining the energy transfer to the load. According to document U.S. Pat. No. 7,830,235, windings are arranged around magnetic gaps, e.g. air gaps, that separate different core elements, which results in additional power losses due to fringing flux around the air gap. Furthermore, core elements with an elaborate shape are used, which will increase manufacturing costs.